REVIEW OF THE CATCH AT AGE OF THE BAY OF BISCAY BLUEFIN TUNA FISHERY ( )

Transcription

1 SCRS/2016/179 Collect. Vol. Sci. Pap. ICCAT, 73(7): (2017) REVIEW OF THE CATCH AT AGE OF THE BAY OF BISCAY BLUEFIN TUNA FISHERY ( ) José L. Cort 1 SUMMARY Based on previously published analytical data, a review is presented of the catch at age (CAA) of the Bay of Biscay bluefin tuna fishery between 1950 and The period between 1950 and 1965 has the least biometric information on the species in this area, and so substitutions have been made using data from later years, for which abundant information is available. The results confirm that the CAA of the juvenile groups (1-4 years) in the first decade of the historical series (1950s) used in the last bluefin tuna stock assessment in 2014 is considerably underestimated, such that the number of juveniles for the period used in the assessment is half that of the values obtained in the present study for the Bay of Biscay fishery alone in the same time period. The scenario is even worse if we consider that, according to a recent publication, approximately 2.8 million one year old specimens would have to be added to the figure presented here, which are absent from the CAA of the last stock assessment, caught using purse seine in the Moroccan Atlantic fisheries between RÉSUMÉ Sur la base des données analytiques publiées précédemment, un examen est présenté de la prise par âge (CAA) de la pêcherie de thon rouge opérant entre 1950 et 2000 dans le Golfe de Gascogne. La période courant entre 1950 et 1965 comporte le moins d information biométrique sur les espèces dans cette zone et c est pourquoi des substitutions ont été faites en utilisant les données des dernières années, pour lesquelles des informations abondantes sont disponibles. Les résultats confirment que la CAA des groupes juvéniles (1-4 ans) dans la première décennie de la série historique (années 50) utilisée dans la dernière évaluation des stocks de thon rouge en 2014 est considérablement sous-estimée, de sorte que le nombre de juvéniles pour la période utilisés dans l'évaluation représente la moitié des valeurs obtenues dans la présente étude pour la seule pêcherie du golfe de Gascogne au cours de la même période. Le scénario est encore pire si l'on considère que, selon une publication récente, environ 2,8 millions de spécimens d'un an devraient être ajoutés au chiffre présenté ici, lesquels sont absents de la CAA de la dernière évaluation des stocks, et ont été capturés à la senne dans les pêcheries marocaines de l'atlantique entre 1958 et RESUMEN Basándose en datos analíticos previamente publicados, se presenta una revisión de la captura por edad (CAA) de la pesquería de atún rojo del golfo de Vizcaya entre 1950 y El periodo entre 1950 y 1965 tiene la menor información biométrica sobre la especie en esta zona y por ello se realizaron sustituciones utilizando los datos de años posteriores, para los que se dispone de abundante información. Los resultados confirman que la CAA de grupos juveniles (1-4 años) en la primera década de la serie histórica (años 50) utilizados en la última evaluación de stock de atún rojo de 2014 está considerablemente subestimada, de tal forma que el número de juveniles para el periodo utilizado en la evaluación es la mitad de los valores obtenidos en este estudio solo para la pesquería del golfo de Vizcaya en el mismo periodo. El escenario es aún peor si consideramos que, de acuerdo con una publicación reciente, deberían añadirse aproximadamente 2,8 millones de ejemplares de un año a la cifra presentada en este estudio, que faltan de la CAA de la última evaluación de stock, capturados mediante cerco en las pesquerías marroquíes del Atlántico entre 1958 y Instituto Español de Oceanografía, Centro Oceanográfico de Santander, Spain (jose.cort@st.ieo.es) 2280

2 KEYWORDS Atlantic bluefin tuna, Bay of Biscay, catch at age statistics Introduction A recent publication on the bluefin tuna, Thunnus thynnus (L.), -ABFT- eastern Atlantic juvenile fisheries (Cort and Abaunza, 2015) reveals that the catches at age (CAA) of groups 1-4 during the first decade of the historical series (1950s) used in the last bluefin tuna stock assessment (ICCAT, 2014a) are substantially underestimated, a fact which undoubtedly creates an unreal vision of its fishing mortality (F 2-5) and of the recruitment in the first years of assessment. A summarized version of the publication (Cort and Abaunza, 2016) was presented at the data meeting of the ABFT Stock Assessment Group of the SCRS (ICCAT, 2016), in which this matter was discussed. The review of the total catches (Task 1) of the Spanish Bay of Biscay fishery (between 1901 and 2000), which was presented to the SCRS in 2014 (Cort et al., 2015), has already been incorporated to the ICCAT database. The review provides details of catches/port of landing, as well as the catches corresponding to the fishery targeting this species and those that form part of non-targeted fishing in the albacore fishery -ALB-, Thunnus alalunga (Bonn.). This paper also contains the overall catches of the fishery, including the catches/year from France. The present study follows the work plan aiming a full revision of the ABFT catch-at-size for the period (Table 14; ICCAT, 2016), in our case of the Bay of Biscay fishery as a whole, i.e. including the data from France and Spain but using the final data referring to CAA. 1 Sources of information and methods 1.1 Data used to estimate CAA in the Bay of Biscay. Why CAA? Le Gall (1950; 1951), Navaz (1950) and Bard et al. (1973) were the first authors to supply biometric data on ABFT in the Bay of Biscay; later, in the papers of Bard et al. (1978), Bard and Cort (1980) and Cort (1990), diverse analyses were presented using historical series of catches (from the 1960s) of the fisheries of the eastern stock using catch-at-size data previously converted to ages through the use of length frequencies and modal values, or age-length keys (ALKs) based on spine readings, a technique developed in the 1980s by Compeán- Jiménez and Bard (1983) which was later applied to Spanish ABFT fisheries by Rey and Cort (1984) and Cort (1990). In a more detailed analysis of the juvenile fisheries of the eastern Atlantic recently carried out using information going back to the beginning of the 1950s, Cort and Abaunza (2015; 2016) used a reviewed version of all the previous information using CAA data at all times. For the elaboration of the demographic structure of the present study ( ), four periods are considered: Very few biometric data of Bay of Biscay ABFT from the 1950s are available, though the information contained in Le Gall (1950; 1951) is enough to know that, since the beginning of the studies of this fishery, this is fundamentally a juvenile fishery with a seasonal period of small spawners (ages 5+) in July and August, as Bard et al. (1973); Cort (1976; 1990) and Cort and Rodríguez-Marín (2009) described years later. The ABFT length distributions published in Cort (1990) were based on the sales sheets from auctions at the Basque port of Ondarroa in 1953 and More recently, in the data review of the Bay of Biscay presented to the Data Recovery Plan of GBYP 02/2011 (Cort and Velasco, 2011), the length distributions for 1953 and 1956 from the same port are also available. The demographic structure of the present study for these two years is based, on one hand, on the catch of the port of Ondarroa (85 t in 1953; and 299 t in 1956, according to Cort et al., 2015), and on the other on the remaining catches, to which the percentage of catch at age of the period has been applied (Table 1, taken from Cort, 1990), a period for which a lot of information is available. For the remaining years to 1965 this latter procedure has been followed. 312,415 ABFT samples were carried out between 1966 and 1986, the mean of which was 12.3 kg (Cort and Abaunza, 2015; 2016), and this is the value that has been applied to estimate the total number of fishes caught each year. 2281

3 The catch-at-size (individual weight) of the ABFT corresponding to the Spanish fleet was obtained from the sales sheets of the port of Ondarroa. The first analytical assessment of the eastern stock in which catch-at-size converted to ages was published in Bard and Cort (1980). The sample size between 1966 and 1970 was 54,982 ABFT. These data were also presented to the GBYP Data Recovery Plan 02/2011. The age of each sampled individual was determined using Table 35 from Cort (1990), which permits the assignation of an age to each ABFT according to the corresponding month and weight for fishes of between 1 and 8 years. The demographic structure of the French catches was determined by taking into account the proportion of ABFT of > 30 kg and of < 30 kg as published in Bard et al. (1978) and the values obtained for the Spanish fleet for ages 1-3 (< 30 kg) and 4-8 (> 30 kg) It was at this time that the systematic collection of sales sheets separated by commercial categories began from auctions at the port of Hondarribia (Fuenterrabía). Using the tables available on page 231 of Cort (1990), age can be assigned according to commercial category. Moreover, from 1972 length sampling began at the port of St. Jean de Luz (Bard et al., 1973) and from 1974 at the port of Hondarribia (Cort and Cendrero, 1975) A sampling network was set up in Spain with the systematic collection of sales sheets by commercial categories from auctions at the port of Hondarribia, length samplings and spine collection for age reading, the collection of logbooks from some vessels from the port of Hondarribia, and the systematic collection began of information on ABFT length samplings from the ports with fleets targeting ALB. From 1985 the age assignation of the samples was performed using annual ALKs created using fin spines readings (Cort, 1990). The CAA of the French catches was obtained from Spanish samplings taking into account the yearly proportion of fish > 30 kg and of < 30 kg. Results Table 1, which summarizes the catches (ages 1-4) in the Bay of Biscay in the period , corresponds to sampling carried out between 1966 and The juvenile catch in this fishery during the study period was 97.5% in number of fishes, age groups 1-3 being the most abundant. The mean weight of the catch throughout the period was 12.3 kg. The actual ABFT catch in this fishery between was 41,086 t, according to Cort et al. (2015) and the catch estimated using the mean weight/age was 40,852 t, just 0.6% lower, which goes to show how good the sample used was. After the present review the results remain the same. Table 2 shows ABFT catches (t) by the targeting and non-targeting ABFT Spanish fleets in the Bay of Biscay ( ). The last column refers to the total value of the catch (France+Spain) throughout the whole area. Table 3 shows ABFT CAA in the Bay of Biscay (France+Spain) from 1950 to Of the total, ABFT juveniles (1-4 years) make up 97.7% of the catch in number of fishes, with age groups 1 and 2 the most numerous at 79.4% of the total number of ABFT caught. The mean weight of the catch in the period was 13.3±4.7 kg, a value that indicates that the mean weight used in estimates of the total catch between 1950 and 1965 (12.3 kg) is within the limits of that estimate. With the exception of 1999, year in which the fleet caught larger fishes (mean weight: 30.4 kg) due to an apparent scarcity of juveniles, or because fishermen moved by commercial interests headed their effort to the larger fish, in the remaining years the mean weight/year of the catch corresponded to specimens of 1-3 years old. Figure 1 shows the overall catch of ABFT in the Bay of Biscay between 1950 and Two phases of maximum catches are seen: and The former coincides with the start of fishing with baitboat in the Bay of Biscay, and the latter with an increase in catches taken by the fleet targeting ALB, mainly vessels from the port of Guetaria in 1996 and

4 Discussion The results of the present study confirm the conclusions of the article by Cort and Abaunza (2015; 2016), which concludes that the CAA of the juvenile groups of 1-4 years in the first decade of the historical series (1950s) used in the last bluefin tuna stock assessment (ICCAT, 2014a) are greatly underestimated. The number of ABFT juveniles (ages 1-4) for the period used in that assessment was 1,860,188, whereas the values obtained in Table 2 (present study), corresponding to ages 1-4 for the same time period, were 3,750,484 individuals. This means that twice as many juveniles were caught in the Bay of Biscay fishery alone that the total number used for the entire eastern stock in the stock assessment of As published in the article by Cort and Abaunza (2015), the juvenile catches by purse seine (PS) in Moroccan Atlantic waters from 1958 would need to be added, a number which, according to the above article, would be in the region of 2.8 million of age 1 fishes during the period This would represent a total catch of 6.5 million juveniles between , a value 3.5 times higher than the figure of 1.9 million used in the 2014 stock assessment. The estimate of Moroccan catches made by Cort and Abaunza (2015; 2016) is based on ICCAT database (2014b) and papers by Fournestin and Dardignac (1962); Aloncle (1966); Dao and Bessineton (1974); Lamboeuf (1975); Brêthes (1978; 1979a, b); Brêthes and Mason (1979), which studied the Moroccan Atlantic ABFT fishery. It can be concluded from these studies that most of the catch taken by the purse seine fleet was made up of 1 year old fishes. According to the analysis of the juvenile ABFT population made by Cort and Abaunza (2015; 2016) for the period , the massive catch of juveniles (ages 1-4) in the Atlantic fisheries of the eastern stock constituted a very considerable fishing mortality (F) with survival rates which, in the most optimistic scenario, were no greater than 16%. This would explain the reason underlying the drastic fall of the eastern Atlantic spawner fisheries from 1963, as occurred in the traps fishery of the strait of Gibraltar and northern European fisheries. These latter collapsed at the beginning of the 1980s and the traps thereafter had yields no more than a quarter of the levels that they obtained prior to the 1960s. In accordance with all seen, it has not sense to keep the selectivity of the Bay of Biscay fishery in 5-6 years old for the period

5 References Aloncle, H. Note sur le thon rouge de la baie Ibero-Marocaine. Bull. l Inst. des Pêches Maritimes du Maroc, 14: (1966). Bard, F. X., C. Bessineton, O. Cendrero, and J. C. Dao. La pêcherie de thon rouge du Golfe de Gascogne. Col. Vol. Sci. Pap. ICCAT, 1: (1973). Bard, F. X, and J. L. Cort. Evaluation du recrutement apparent du thon rouge (Thunnus thynnus) en Atlantique Est a l Ouest de Gibraltar. Col. Vol. Sci. Pap. ICCAT, 9 (2): (1980). Bard, F. X., J. L. Cort, and J. C. Rey. Commentaires sur la composition demographique des pêcheries de thon rouge (Thunnus thynnus) de l Est Atlantique et de la Méditerranée. Col. Vol. Sci. Pap. ICCAT, 2: (1978). Brêthes, J. C. Campagne de marquage de jeunes thons rouges au large des côtes du Maroc. Col. Vol. Sci. Pap. ICCAT, 7: (1978). Brêthes, J. C. Sur les premiers recuperations des thons rouges marqués en juillet 1977 au large du Maroc. Col. Vol. Sci. Pap. ICCAT, 8: (1979a). Brêthes, J. C. Essai d estimation d une prise para unité d effort pour la pêcherie de surface au thon rouge a Casablanca (Maroc). Col. Vol. Sci. Pap. ICCAT, 8: (1979b). Brêthes, J. C., and J. M. Mason Jr. Bluefin tuna tagging off the Atlantic coast of Morocco in Col. Vol. Sci. Pap. ICCAT, 8: (1979). Compeán-Jiménez, G., and F. X. Bard. Growth increments on dorsal spines of eastern Atlantic bluefin tuna (Thunnus thynnus (L.)) and their possible relation to migrations patterns. NOAA Tech. Rep. NMFS, 8: (1983). Cort, J. L. Datos sobre la biología y pesca del atún rojo (Thunnus thynnus, L.) en el golfo de Vizcaya. Campaña de 1975 en el puerto de Fuenterrabía. Col. Vol. Sci. Pap. ICCAT, 5 (2): 241 (1976). Cort, J. L. Biología y pesca del atún rojo, Thunnus thynnus (L.), del mar Cantábrico. Publicaciones Especiales Inst. Esp. Oceanog., Num. 4: 272 p. (1990). Cort, J. L., and P. Abaunza. The fall of the tuna traps and the collapse of the Atlantic bluefin tuna, Thunnus thynnus (L.), fisheries of northern Europe from the 1960s. Reviews in Fisheries Science & Aquaculture, 23 (4): (2015). Cort, J. L., and P. Abaunza. (in press). The impact of massive fishing of juvenile Atlantic bluefin tunas on the spawning population ( ). ICCAT, Document SCRS/2016/151, 35 p. (2016). Cort, J. L., I. Artetxe, and J. Santiago. Review of bluefin tuna, Thunnus thynnus (L.), catches made by Spanish bait boat fleet in the Bay of Biscay during 20 th century. Col. Vol. Sci. Pap. ICCAT, 71 (3): (2015). Cort, J. L., and O. Cendrero. La pesca del atún rojo (Thunnus thynnus, L.) en el golfo de Vizcaya (1974). Col. Vol. Sci. Pap. ICCAT, 4: (1975). Cort, J. L., and E. Rodríguez-Marín. The bluefin tuna (Thunnus thynnus) fishery in the Bay of Biscay. Evolution of 5+ group since ICCAT, World Symposium for the Study into the Stock Fluctuation of Northern Bluefin Tunas (Thunnus thynnus and Thunnus orientalis) Including the Historic Periods. Col. Vol. Sci. Pap. ICCAT, 63: (2009). Cort, J. L., and M. Velasco. Plan de Recuperación de Datos, GBYP 02/2011. Informe Final, septiembre, 2011, 10 p Dao, J. C., and C. Bessineton. Quelques données sur l exploitation du thon rouge (Thunnus thynnus) dans l Atlantique Nord. Col. Vol. Sci. Pap. ICCAT, 2: (1974). 2284

6 Furnestin, J., and J. Dardignac. Le thon rouge du Maroc Atlantique (Thunnus thynnus Linné). Trav. Inst. Pêches Marit., 26: (1962). ICCAT. Report of 2014 Atlantic bluefin tuna stock assessment session. Madrid, Spain, 22 to 27, 2014; 178 p. (2014a). Available from: ICCAT Database, version 10. Available from: (2014b). ICCAT. Report of the 2016 ICCAT Bluefin data preparatory meeting. Madrid, Spain July, 2016 (2016). Available from: Lamboeuf, M. Contribution a la connaissance des migrations des jeunes thons rouges a partir du Maroc. Col. Vol. Sci. Pap. ICCAT, 4: (1975). Le Gall, J. Le thon rouge (Thunnus thynnus L.) dans les parages de Saint Jean de Luz, en Ann. Biol. Cons. Int. Expl. Mer, 6: (1950). Le Gall, J. Le thon rouge (Thunnus thynnus L.) dans le Golfe de Gascogne en Ann. Biol. Cons. Int. Expl. Mer, 8: (1951). Navaz, J. M. Le thon de la côte basque. Ann. Biol. Cons. Int. Expl. Mer, 6: (1950). Rey, J. C., and J. L. Cort. Una clave talla/edad por lectura de espinas para el atún rojo (Thunnus thynnus, L.) del Atlántico Este. Col. Vol. Sci. Pap. ICCAT 20: (1984). 2285

7 Table 1. Summary of the demographic structure of ABFT catches in the Bay of Biscay between 1966 and 1986 (Cort, 1990). Actual catch ( ): 41,083 t Age Total N 1,194,522 1,428, , ,345 50,689 18,379 8,531 4,293 3,329,176 % Mean weight (kg)/age Inferred W (kg) 5,972,610 14,994,084 9,127,771 5,340,765 2,787,895 1,341, , ,109 40,851,815 W (t) 5,973 14,994 9,128 5,341 2,788 1, ,852 Table 2. ABFT catches (t) by the targeting and non targeting ABFT Spanish fleets in the Bay of Biscay. Right column, total catch in all the area (taken from Cort et al., 2015). IEO and AZTI-Tecnalia Stock ATE ATE ATE ATE Area NE NE Bay of Biscay Bay of Biscay GearGrp BB BB BB BB Year/Fleet EU.ESP-ES- CANT_ABFT EU.ESP-ES- CANT_ALB TOTAL, Spain Spain+France , ,106 2, , , ,323 4, , ,771 4, , ,049 5, , ,528 6, , ,956 3, , ,467 4, , ,938 4, , ,769 3, , , , , , ,166 1, , ,711 3, , , ,226 1, , ,635 2, , ,575 2, , ,362 2, , ,870 2, , ,126 1, ,220 1, , , ,199 1, , ,799 2, , ,173 1, ,026 1, ,114 1,245 2,359 2, , ,365 2, , ,848 2, , ,875 2, , ,513 2, , ,082 2, , ,113 2, , ,493 2, ,141 1, ,017 1, , ,540 4, , ,294 1, , ,772 3, , ,723 5, , ,060 6, , ,512 3, , ,194 1, ,219 1,761 IEO s historic data (Cort, 1990), contrasted and complemented by AZTI-Tecnalia s data AZTI-Tecnalia s data complemented by IEO s data 2286

8 Table 3. ABFT CAA (number of fish, N) in the Bay of Biscay (France+Spain), AGE Year B of B (t) (Cort et al., 2015) Total (N) ,975 86, ,769 34,832 10,401 3,628 1, , , , ,048 45,331 13,536 4,722 1, , , , ,410 54,851 16,379 5,714 2,285 1, , , , ,979 50,102 14,684 4,996 1, , , , ,838 64,393 19,229 6,708 2,683 1, , , , ,767 76,789 22,930 7,999 3,200 1, , ,409 80,614 96,333 32,336 14,548 8,688 2, , , , ,105 47,028 14,043 4,899 1, , , , ,010 50,353 15,036 5,245 2,098 1, , , , ,537 44,488 13,285 4,634 1, , ,374 40,103 47,922 16,086 4,803 1, , ,597 46,625 55,716 18,702 5,585 1, , ,702 49,676 59,362 19,926 5,950 2, , ,381 40,307 48,167 16,168 4,828 1, , ,260 36,776 43,946 14,751 4,405 1, , ,787 52,157 62,327 20,921 6,247 2, , ,335 9,357 88,389 88,157 19, , ,771 3,536 28,730 56,641 6, , ,314 10,463 25,083 15,880 15,543 2, , ,760 34,554 90,327 16,640 5,074 1, , ,367 44,272 97,729 24,620 7,274 3,695 1, , ,255 5,953 74,172 12,349 5,963 8,784 3,468 1, , ,102 17,500 58,080 21,606 2,828 6,802 3,151 1,728 1, , ,421 20,044 87,114 6,145 2,489 5,929 4,592 2,767 2, , ,648 17,513 67,129 28,786 3,380 1, , ,912 34, ,103 11,321 5,728 1, , ,012 1,237 56,327 12,880 2,323 1, , ,791 35,107 90,305 20,618 6, , , ,820 66,970 9,813 14,252 3, , ,448 38,234 13,318 15,798 14,676 3, , ,286 41,962 32,255 10,649 3,908 3,116 1, , ,078 38,247 3,902 1, , ,728 33,033 9,389 3, , , ,517 53,040 18,346 1, , ,967 56, ,317 40,968 5,144 1, , ,338 17,738 97,035 47,611 7,821 1, , , ,519 57,236 7,942 8, , ,046 47, ,488 8,289 4,430 2, , , ,484 74,779 11,699 2, , , , ,038 10,472 3, , , ,827 48,222 23,799 7,806 1, , ,706 57,528 82,276 11,388 6,095 1, , ,911 62, ,356 19,488 2, , ,639 47, ,103 66,767 18,265 2, , ,630 37,981 37,289 26,749 13, , , , ,537 44,789 3, , , , ,627 62,698 31,436 7, , , ,795 71, ,989 42,568 7, , ,125 59,534 61,412 19,013 39,580 4, , ,782 14,450 6,354 4,519 17,217 14,219 1, , ,761 65,240 26,492 9,446 5,488 6,502 5, ,100 Total 134,532 4,502,744 4,415,206 1,536, , ,758 54,834 22,500 9,129 11,238,

9 Catch (fish) 550, , , , , , , , ,000 55, Figure 1. Catches of ABFT in the Bay of Biscay ( ). 2288